1. Field of the Invention
The present invention relates to a dehumidifying material capable of exhibiting excellent dehumidifying performance in a wide humidity environment range from a low humidity to a high humidity, a dehumidifying element supporting the dehumidifying material and a manufacturing method therefor.
2. Description of the Related Art
Hitherto, a honeycomb structure supporting a dehumidifying material, such as silica gel or zeolite, has widely been employed as a dehumidifying element.
When a comparison is made between silica gel and zeolite, zeolite exhibits greater quantity of dehumidification in an environment of a low humidity. In an environment of a high humidity, silica gel exhibits greater quantity of dehumidification. Therefore, use of the foregoing dehumidifying elements has separably been employed to be adaptable to the environment of the humidity.
From a viewpoint of cost reduction, silica gel can easily be prepared. Moreover, silica gel exhibits a low temperature required when it is prepared and, therefore, only a low running cost is required. Hence it follows that a considerably effective dehumidifying element can be obtained when the dehumidifying performance of silica gel can be improved in an environment of a low humidity.
In view of the foregoing, an object of the present invention is to provide a dehumidifying material capable of exhibiting excellent dehumidifying performance regardless of environment of humidity, a dehumidifying material element and a method capable of manufacturing the material and the element.
To achieve the foregoing object, according to one aspect of the present invention, there is provided a dehumidifying material comprising: 90.0 parts by weight to 99.9 parts by weight of silicon dioxide which is silica gel; and 0.1 part by weight to 10.0 parts by weight of an iron oxide or a mixture of the iron oxide and another metal oxide and a dehumidifying element incorporating a support member constituted by an inorganic fiber sheet and supporting the dehumidifying material.
To achieve the object, according to another aspect of the invention, there is provided a method of manufacturing a dehumidifying element comprising the steps of: allowing alkali silicate or alkokysilane to adhere to an inorganic fiber sheet to gel the inorganic fiber sheet; immersing the inorganic fiber sheet in solution containing iron salt or iron and other metal salt; and drying the inorganic fiber sheet.
The present invention is arranged such that alkali silicate, alkoxysilane or their polymer is employed as a silica gel source. A catalyst is added to the silica gel source when reactions, such as hydrolysis, are performed so that a gel material is prepared. Then, solution (hereinafter called xe2x80x9cmetal salt solution) containing iron salt or the iron salt and another metal salt is added to the foregoing gel material to introduce metal ions into the gel. Then, the gel material is dried so that silica gel of a composite metal oxide is obtained which is a dehumidifying material according to the present invention and which is composed of the iron oxide or the composite material of the iron oxide and another metal oxide.
When a dehumidifying element is required, an inorganic fiber sheet to which alkali silicate or alkoxysilane has been allowed to adhere is gelled by performing hydrolysis in the presence of a catalyst. Then, the sheet is immersed in metal salt solution, and then the sheet is dried. Thus, the dehumidifying element incorporating the inorganic fiber sheet supporting the silica gel of a composite metal oxide can be obtained.
The inorganic fiber sheet is obtained by forming ceramic fibers or glass fibers into a sheet shape by using a binder. From a viewpoint of practical use, it is preferable that the inorganic fiber sheet is formed into a honeycomb shape.
The alkali silicate is exemplified by sodium silicate, lithium silicate, potassium silicate or their composite materials.
Alkoxysilane is a compound expressed by general formula Si (OR1)4 (where R1 is an alkyl group). Specifically, alkoxysilane is exemplified by tetramethoxysilane, tetraethoxysilane, tetra n-propoxysilane, tetra n-butylsilane and their polymers.
When the gelling operation is performed by using alkali silicate, acidic solution is directly added to alkali silicate. As an alternative to this, the acidic solution is added to solution in which alkali silicate is diluted with water. When the dehumidifying element is manufactured, alkali silicate is diluted with water. Then, the solution is allowed to adhere to an inorganic fiber sheet. Then, the inorganic fiber sheet is immersed in acidic solution so as to be gelled. A preferred acidic solution is solution of strong acid, such as sulfuric acid, hydrochloric acid or nitric acid.
The reaction is performed under condition that the pH is 0 to 2.5, more preferably 0 to 1.5. When the foregoing pH range is satisfied, sodium and the like in the silica gel can easily be desorbed. Moreover, deterioration in the fibers can be prevented when the inorganic fiber sheet, in particular, a glass fiber sheet is employed. The temperature at which the reactions are performed may be included in a range from 0xc2x0 C. to 100xc2x0 C. Since reactions are performed too fast in a hot environment, it is preferable that the temperature is about 30xc2x0 C. to 60xc2x0 C.
When alkoxysilane is employed, alkoxysilane is used as it is or alkoxysilane is diluted in hydrophilic organic solvent. The organic solvent is exemplified by alcohol, such as methanol, ethanol, propanol or butanol; tetrahydrofuran or dioxane. Then, hydrolysis solution containing acid, a base and water added thereto is added to the hydrophilic organic solvent to perform the gelling operation. When the dehumidifying element is obtained, solution obtained by diluting alkoxysilane with hydrophilic organic solvent is allowed to adhere to the inorganic fiber sheet. Then, the inorganic fiber sheet is immersed in the foregoing hydrolysis solution so as to be gelled. The acid to be employed is exemplified by the foregoing strong acid. The base is exemplified by sodium hydroxide, potassium hydroxide and ammonia.
The gel material or the inorganic fiber sheet supporting the gel material is cleaned, and then brought into contact with metal salt solution in a state where the inorganic fiber sheet is in the wet state. Thus, iron ions and iron ions and other metal ions are introduced into the gel. It is preferable that the metal except for iron is magnesium, zinc, copper, nickel, manganese, zirconium, aluminum or titanium.
The iron ion source is exemplified by solution containing iron salt, such as iron sulfate, iron ammonium sulfate, iron ammonium citrate or iron ammonium oxalate. Another metal ion source is exemplified by solution containing metal salt, such as magnesium sulfate, magnesium acetate, zinc sulfate, zinc acetate, copper sulfate, copper acetate, nickel sulfate, ammonium nickel sulfate, nickel acetate, manganese acetate, manganese ammonium acetate, manganese sulfate, zirconium sulfate, aluminum sulfate, titanium sulfate or titanium chloride.
When other metal ions are introduced together with iron ions, the gel material may be brought into contact with iron salt solution. Then, the gel material is brought into contact with the other metal salt solution. As an alternative to this, mixed solution of iron salt and the other metal salt may be brought into contact with the gel material. The concentration of the iron ion solution and that of the other metal salt solution may arbitrarily be determined to satisfy a range from 0.01 wt % to the saturated solubility of each solution. It is preferable that the concentration is 0.1 wt % to 20 wt %. When iron ions and other metal ions are introduced, the ratio of the two types of ions is adjusted such that other metal ions is 1 mole or lower with respect to one mole of iron ions.
Since introduction of ions above can quickly be completed, time for which contact with the gel material is established may be several minutes. To obtain a uniform material, it is preferable that the contact is established for one or more hours.
After iron ions and metal ions have been introduced, cleaning and drying are again performed. Thus, the dehumidifying material or the dehumidifying element according to the present invention can be obtained. The product is a composite material of an iron oxide and silica gel or a composite material of the iron oxide, another metal oxide and silica gel.
The product is usually dried with hot air. When freeze-drying or freeze vacuum drying is performed, drying can be performed without any breakage of pores of the gel material. Thus, a satisfactory composite material can be obtained.